1. Field of the Invention
The invention relates to a microwave oven comprising a microwave source and defrosting detector arranged in the oven in the proximity of a product to be processed, the detector comprising a material which absorbs microwave energy, the absorption of microwave energy by the detector and by the product causing their temperatures to rise, the detector temperature being measured by means of a measuring element.
2. Description of the Related Art
Currently microwave ovens are often used for defrosting and re-heating foodstufs which have been previously kept in a freezer. In general, this defrosting is effected empirically: the user determines the approximate weight of the food to be defrosted in order to derive an approximate operating time for the microwave oven. This results in more or less complete defrosting or even a beginning of cooking. It is also known from the literature that around 2.45 GHz the microwave absorption considerably depending on whether the water temperature is below or above 0.degree. C., Below 0.degree. C. ice forms which is highly transparent to microwaves, while at a temperature above 0.degree. C. water has a very strong microwave absorption. This effect is caused by variations of the dielectric losses of water as a function of temperature.
French patent No. FR 2,571,830 describes a microwave oven provided with a standard load placed in the oven beside the food to be processed. The standard load absorbs microwave energy in accordance with a distribution which depends on the standard load and on the load of food to be processed. Thus, from the rise in temperature of the standard load it is possible to derive the quantity of food present in the oven and to automatically determine the cooking time. According to said patent the rate of heating of the standard load is substantially independent of the temperature of the detector.
Although a defrosting operation is mentioned therein said patent does not reveal any means for attending the critical transition from a frozen condition to a defrosted condition of the food to be processed, or how the defrosting can be controlled.